CN103034016B - All-optical analog-to-digital conversion design method - Google Patents

Abstract

The invention discloses an all-optical analog-to-digital conversion design method. The method comprises the following specific steps of: multiplexing light generated by a multi-wave-length pulse light source onto the same light path through a multiplexer; re-partitioning the light path into two paths through a 1*2 multi-mode interference coupler, sampling an input analog optical signal through a phase modulator in one path, entering one access port of the multi-mode interference coupler, and directly injecting the other path into the other access port of the multi-mode interference coupler; demultiplexing light output from the output port of the multi-mode interference coupler onto light channels of different wavelengths through a demultiplexer; and receiving, amplifying and deciding an optical signal output by the demultiplex in sequence through a photoelectric detector, an amplifier and a decision device to obtain a digital output signal. An entire all-optical analog-to-digital conversion system can be integrated onto a miniature photon integrated loop chip or a silicon-based waveguide chip, large-scale production can be realized, the cost is low, and the development of the information industry is promoted.

Description

A kind of full optical analog to digital conversion method for designing

Technical field

The present invention relates to optical analogy/digitizer technology field, be specifically related to a kind of full optical analog to digital conversion method for designing based on multi-mode interference coupler and multiplexing demultiplexing device.

Background technology

Along with the information age of modern society entry altitude, the signal bandwidth of the required process of all trades and professions is doubled and redoubled, electronic analogue-to-digital converter is more and more difficult to the demand meeting now current various ultra broadband and high-speed applications, as fields such as phased-array radar, imaging of medical, radioastronomy, electronic warfare, ULTRA-WIDEBAND RADAR reception and software radios.Thus utilize optical analog-to-digital converter to replace electronic analogue-to-digital converter, realizing the high-precision analog to digital conversion of hypervelocity becomes one of current optoelectronic areas and studies hot topic greatly.At present, foremost full optical analog to digital conversion scheme has three kinds: a kind of scheme being the numeral utilizing the intensity modulator array with different half-wave modulation voltage radio frequency analog input signal to be converted to Gray code and exporting, the shortcoming of such full optical analog to digital conversion scheme is that required modulator number is directly proportional to quantization digit, causes its cost high; The half-wave voltage of most significant digit modulator increases with the raising exponentially of quantified precision, which limits the quantified precision that the program cannot reach high, and need the simulating signal of carrying out changing to be loaded concurrently on each modulator, the raising synchronously limiting quantified precision of signal.The second is the phase-shift optical quantization scheme utilizing space interference, and the stability due to space interference in this kind of scheme is poor, and whole system needs fabulous mechanical stability, so system quantifies performance is difficult to ensure; When the number of detector is many, between them, the adjustment of relative position is very difficult, which limits the raising of the quantified precision of system; Owing to being space interference, system is difficult to integrated, and practical value is little.Last class is by utilizing some nonlinear effect to become certain change spectrally to carry out optical spectrum encoded full optical analog to digital conversion scheme the intensity-conversion of electric signal to be measured, the nonlinear effect utilized in this kind of scheme all proposes very high requirement to sampling pulse, and the spectrum change rate that nonlinear effect can realize is very limited, these schemes are all difficult to reach high quantified precision.Above shortcoming limits the practical of these all-light analog-digital converter schemes.

Summary of the invention

(1) technical matters that will solve

The present invention mainly solve full optical analog to digital conversion cost in prior art high, be difficult to integrated, high and need the problem in sampling pulse source of substantial amounts to the mechanical stability requirements of system.The invention provides a kind of full light phase-shift optical quantization analog to digital conversion method for designing based on multi-mode interference coupler (multiple-mode interfence) and multiplexing demultiplexing device (MUX/DMUX), the method is easy to use, extendability and compatible strong, with low cost, noiseproof feature is strong, mechanical stability is strong, and related device integrability, military and commercialization has a extensive future.

(2) technical scheme

The invention provides a kind of full optical analog to digital conversion method for designing, comprise the following steps:

S1, by multi-Wavelength Pulses light source produce multiplex pulse light be multiplexed in same light path by multiplexer;

S2, by 1 × 2 multi-mode interference coupler, above-mentioned light path is divided into 2 tunnels again, the analog optical signal of phase-modulator to input of wherein leading up to is sampled, enter in an access interface of multi-mode interference coupler afterwards, another access interface of multi-mode interference coupler is directly injected on another road;

S3, be demultiplexed on the optical channel of different wave length by the light that the output port from described multi-mode interference coupler exports through demodulation multiplexer, the light signal exported from described demodulation multiplexer is exactly the light signal after being quantized and encoding;

S4, the light signal using photodetector, amplifier and decision device to export described demodulation multiplexer successively receive, amplify and adjudicate, and obtain binary digital output signals.

Preferably, described multi-mode interference coupler is 4 × 4 multi-mode interference couplers or 8 × 8 multi-mode interference couplers.

Preferably, described multi-Wavelength Pulses light source is realized by Mode-locked laser device.

Preferably, described multiplexer/demultiplexer is realized by array waveguide grating.

Preferably, described phase-modulator is realized by electroded active optical waveguide.

Preferably, by increasing the sampling pulse source number of different centre wavelength or increasing the number of multi-mode interference coupler, analog-to-digital quantified precision can be improved.

Preferably, the device that the method uses can realize integrated on InP-base, GaAs base or Si base.

Preferably, the quantification of the method and cataloged procedure are realized by 4 × 4 multi-mode interference couplers or 8 × 8 multi-mode interference couplers.

Preferably, described 4 × 4 multi-mode interference couplers or the input waveguide of 8 × 8 multi-mode interference couplers and the selection of output waveguide have following rule:

For 4 × 4 multi-mode interference couplers, its input waveguide is combined as the 1st passage and the 3rd passage, or the 2nd passage and the 4th passage, and its output waveguide is combined as the 1st passage and the 3rd passage, or the 2nd passage and the 4th passage;

For 8 × 8 multi-mode interference couplers, its input waveguide is combined as the 1st passage and the 3rd passage, or the 6th passage and the 8th passage, and its output waveguide is combined as 1,2,3,4 four passage, or 5,6,7,8 four passages.

(3) beneficial effect

The inventive method by the whole full optical analog to digital conversion system integration to integreted phontonics loop (PIC) chip of a very small dimensions or SOI silica-based waveguides chip top, can be able to be produced in enormous quantities, with low cost, effectively promotes the development of information industry.

Accompanying drawing explanation

Fig. 1 is the process flow diagram of the inventive method;

Fig. 2 is 4 the full optical analog to digital conversion systematic schematic diagrams that the present invention is based on single 4 × 4 multi-mode interference couplers;

Fig. 3 is the quantization encoding family curve of 4 the full optical analog to digital conversion systems that the present invention is based on single 4 × 4 multi-mode interference couplers;

Fig. 4 is 5 the full optical analog to digital conversion systematic schematic diagrams that the present invention is based on single 8 × 8 multi-mode interference couplers;

Fig. 5 is the quantization encoding family curve of 5 the full optical analog to digital conversion systems that the present invention is based on single 8 × 8 multi-mode interference couplers;

Fig. 6 is the core component figure of 5 all-light analog-digital converters that the present invention is based on 24 × 4 multi-mode interference couplers and the injection of 4 wavelength mode-locked lasers;

Fig. 7 is the core component figure of 6 all-light analog-digital converters that the present invention is based on 28 × 8 multi-mode interference couplers and the injection of 4 wavelength mode-locked lasers.

1. semiconductor mode-locked pulsed lasers in figure, 2.1 × n multiplexer, 3. simulating signal, 4.1 × 23dB multi-mode interference coupler, 5. phase-modulator, 6.4 × 4 multi-mode interference couplers, 7.n × 1 demodulation multiplexer, 8. photodetector, 9. amplifier, 10. comparer, 11. core components, 12. phase shift Optical Samplings and light quantization module, 13. electric judging module, the 14. passive phase shift waveguides in π/4,15.8 × 8 multi-mode interference couplers, the 16. passive phase shift waveguides in π/8.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples for illustration of the present invention, but are not used for limiting the scope of the invention.

Fig. 1 is the process flow diagram of the inventive method, the invention provides a kind of full optical analog to digital conversion method for designing, comprises the following steps:

S1: the multiplex pulse light produced from multi-Wavelength Pulses light source is multiplexed on the way by multiplexer (MUX);

S2: then by 1 × 2 multi-mode interference coupler, this road is divided into 2 tunnels again, the analog radio-frequency signal of phase-modulator to input of wherein leading up to is sampled, then enter in an access interface of 4 × 4 multi-mode interference couplers (or 8 × 8 multi-mode interference couplers), another corresponding access interface of 4 × 4 multi-mode interference couplers (or 8 × 8 multi-mode interference couplers) is directly injected on another road;

S3: the light exported from 4 × 4 multi-mode interference couplers (or 8 × 8 multi-mode interference couplers) each passage is demultiplexed into via demodulation multiplexer the subchannel of the different wave length corresponding to it again;

Because the injection light of phase-modulator to different wave length can produce different extra phase shift, and 4 × 4 transport propertys of multi-mode interference coupler (or 8 × 8 multi-mode interference couplers), the light signal exported from demodulation multiplexer (DMUX) subchannel is exactly the light signal being quantized and encoding.

S4: and then through the judgement of the reception of photodetector (Photodetector), the amplification of amplifier (Amplifiier) and decision device (comparator), belt code (Circular Code) binary digit that just can obtain reaction simulation input signal strength exports.

Wherein Optical Sampling process is realized by phase-modulator, and light quantization and coding 4 × 4 multi-mode interference coupler (or 8 × 8 multi-mode interference couplers) realize.Device involved by whole Optical Sampling and light quantization process all can be realized, so the program can realize integrated on InP-base, GaAs base or Si base by III-VI race's semiconductor devices or silicon-based devices.Whole light path is carried out all in the waveguide, and system mechanics stability is very strong.And be passive wave guide device owing to quantizing 4 × 4 multi-mode interference couplers (or 8 × 8 multi-mode interference couplers) that adopt of nucleus module, process allowance is good, responsive hardly to optical wavelength, size is little, loss is little, and only use a phase-modulator, make whole system have very high bandwidth sum noise immunity.Attain to a high place the analog to digital conversion of quantified precision, only need 4 × 4 multi-mode interference couplers (or 8 × 8 multi-mode interference couplers) number increased in phase shift Optical Sampling and quantization modules (PSOSQM) or the number increasing different wave length sampling pulse source, so the compatibility of whole system and extendability extremely strong.In addition, what whole system was used is all simple Devices, wherein, multi-Wavelength Pulses light source can be realized by Mode-locked laser device (MLL), multiplexing demultiplexing device (MUX/DMUX) can be realized by array waveguide grating (AWG), and phase-modulator only needs the active waveguide adding electrode with a section to realize.So in production in enormous quantities situation, the full optical mode number converter in the present invention is with low cost, and military and commercialization has a extensive future.

With embodiment, the present invention is set forth below:

The invention provides a kind of method for designing of the all-light analog-digital converter based on 4 × 4 multi-mode interference couplers or 8 × 8 multi-mode interference couplers.

1, as follows based on the principle of work of the full optical analog to digital conversion system of 4 × 4 multi-mode interference couplers shown in Fig. 2:

When phase-modulator (5) is for lithium niobate phase modulator (phase-modulator also can be the semiconductor modulator of silica-based phase-modulator or III-VI race's material), lithium niobate (LiNbO can be obtained according to Sellmeier equation ₃) refractive index of phase-modulator (5) and the relational expression of lambda1-wavelength be:

$n_o^2\left(\mathrm{\λ}\right)=4.9048+\frac{0.11768}{{\mathrm{\λ}}^2-0.0475}-0.027169{\mathrm{\λ}}^2$

$n_e^2\left(\mathrm{\λ}\right)=4.5820+\frac{0.099169}{{\mathrm{\λ}}^2-0.04443}-0.02195{\mathrm{\λ}}^2$

Wherein n _oand n _erefer to the refractive index of ordinary light (o light) and non-ordinary light (e light) respectively, the unit of wavelength X is um.Suppose polarization direction and the LiNbO of the sampled light pulse that semiconductor mode-locked pulsed laser (1) produces ₃the a certain major axes orientation of phase-modulator (5) is identical (assuming that main shaft is o light direction), and the pulse signal E that the injection side of 4 × 4 multi-mode interference couplers (6) is modulated through phase-modulator (5) _swith not through pulse signal E that phase-modulator (5) is modulated _ptime domain waveform be following form:

In formula, P _p, ω _p, refer to E respectively _pluminous power, circular frequency and initial phase, P _s, ω _s, refer to E respectively _pluminous power, circular frequency and initial phase, so the pulse signal E that modulates through phase-modulator (5) of the injection side of 4 × 4 multi-mode interference couplers (6) _swith not through pulse signal E that phase-modulator (5) is modulated _pphase differential can be expressed as:

n=1,2,3,...

Wherein, V _sfor the instantaneous voltage of the upper added simulating signal (3) of phase-modulator (5), V _πfor the half-wave modulation voltage of phase-modulator (5), L is the effective length of lithium columbate crystal in phase-modulator (5), λ _nbe the wavelength of the n-th mode-locked laser (1), n ₀(λ _n) for lithium columbate crystal in phase-modulator (5) be λ for centre wavelength _nthe refractive index of its correspondence of light.The output signal normalized amplitude of semiconductor mode-locked pulsed laser (1) gained after 4 × 4 multi-mode interference couplers (6) is:

In formula, κ ₄₄it is point backscatter extinction logarithmic ratio of 4 × 4 multi-mode interference couplers (6).Assuming that P _p=P _s, κ ₄₄=1/4, and selected semiconductor mode-locked pulsed laser (1) each wavelength meets following condition:

$\frac{2\mathrm{\π}}{{\mathrm{\λ}}_{n-1}}\·n_o\left({\mathrm{\λ}}_{n-1}\right)\·L-\frac{2\mathrm{\π}}{{\mathrm{\λ}}_n}\·n_o\left({\mathrm{\λ}}_n\right)\·L=\frac{\mathrm{\π}}{2^{N_b-1}}$

In formula, N _bfor the quantified precision of this A/D conversion system.Then from the light signal be through quantizing that each n × 1 demodulation multiplexer (7) different wave length channel exports, it is converted into electric signal through photodetector (8), send in comparer (10) and adjudicate after being amplified by amplifier (9), gained exports the scale-of-two be through reaction simulation signal (3) Real-time intensity of coding and to go in ring code.For 4 wavelength, namely during semiconductor mode-locked pulsed laser (1) medium wavelength number n=4, quantification and the encoding characteristics of the scheme of ADC shown in Fig. 2 can be expressed as shown in Figure 3.

When carrying out the upgrading of quantified precision to the A/D conversion system described in Fig. 2, first method the core component (11) in low-order system is replaced with the multi output passage core component (11) with certain phase shift relation produced by multiple 4 × 4 multi-mode interference couplers (6) cascade, and cascade m 4 × 4 multi-mode interference couplers (6) need use 1 × m multi-mode interference coupler (4) and passive phase shift waveguide.The number of corresponding n × 1 demodulation multiplexer (7) increases along with the increase of digital output channel number.Second method is the number increasing different wave length laser instrument in semiconductor mode-locked pulsed laser (1).The third method is the number both having increased different wave length laser instrument in semiconductor mode-locked pulsed laser (1), again core component (11) is replaced with the high-order quantization system produced by multiple 4 × 4 multi-mode interference coupler cascades.Such as, be promoted to 5 quantified precisions by 4 quantified precisions, the core component (11) in Fig. 2 can be replaced with the core component shown in Fig. 6 according to first method, the passive phase shift waveguide used by cascade is the passive phase shift waveguides (14) in π/4; Second method is for being increased to 8 by the number of different wave length laser instrument in semiconductor mode-locked pulsed laser (1) by 4; Core component (11) in Fig. 2 is replaced with the core component shown in Fig. 6 according to the third method simultaneously, and the number of different wave length laser instrument in semiconductor mode-locked pulsed laser (1) is increased to 8 by 4, then the quantified precision theoretical value of gained A/D conversion system is 6.By that analogy, the final quantization precision N of system _bwith 4 × 4 multi-mode interference couplers (6) quantity N used in semiconductor mode-locked pulsed laser (1) wavelength number n and core component (11) _{multiple-mode interfence 4 × 4}relation be shown below:

N _b=log ₂(4N _MMI4×4·n),N _MMI4×4=1,2,3,...,n=1,2,3,...

2, shown in Fig. 4, the principle of work of 5 full optical analog to digital conversion systems is as follows:

When phase-modulator (5) is for lithium niobate phase modulator (phase-modulator also can be the semiconductor modulator of silica-based phase-modulator or III-VI race's material), lithium niobate (LiNbO can be obtained according to Sellmeier equation ₃) refractive index of phase-modulator (5) and the relational expression of lambda1-wavelength be:

$n_o^2\left(\mathrm{\λ}\right)=4.9048+\frac{0.11768}{{\mathrm{\λ}}^2-0.0475}-0.027169{\mathrm{\λ}}^2$

$n_e^2\left(\mathrm{\λ}\right)=4.5820+\frac{0.099169}{{\mathrm{\λ}}^2-0.04443}-0.02195{\mathrm{\λ}}^2$

Wherein n _oand n _erefer to the refractive index of o light and e light respectively, the unit of wavelength X is um.Suppose polarization direction and the LiNbO of the sampled light pulse that semiconductor mode-locked pulsed laser (1) produces ₃the a certain major axes orientation of phase-modulator (5) is identical (assuming that main shaft is o light direction), and the pulse signal E that the injection side of 8 × 8 multi-mode interference couplers (15) is modulated through phase-modulator (5) _swith not through pulse signal E that phase-modulator (5) is modulated _ptime domain waveform be following form:

In formula, P _p, ω _p, refer to E respectively _pluminous power, circular frequency and initial phase, P _s, ω _s, refer to E respectively _pluminous power, circular frequency and initial phase, so the pulse signal E that modulates through phase-modulator (5) of the injection side of 8 × 8 multi-mode interference couplers (15) _swith not through pulse signal E that phase-modulator (5) is modulated _pphase differential can be expressed as:

n=1,2,3,...

Wherein, V _sfor the instantaneous voltage of the upper added simulating signal (3) of phase-modulator (5), V _πfor the half-wave modulation voltage of phase-modulator (5), L is the effective length of lithium columbate crystal in phase-modulator (5), λ _nbe the wavelength of the n-th mode-locked laser (1), n ₀(λ _n) for lithium columbate crystal in phase-modulator (5) be λ for centre wavelength _nthe refractive index of its correspondence of light.The output signal normalized amplitude of semiconductor mode-locked pulsed laser (1) gained after 8 × 8 multi-mode interference couplers (15) is:

In formula, κ ₈₈it is point backscatter extinction logarithmic ratio of 8 × 8 multi-mode interference couplers (6).Work as P _p=P _s, κ ₈₈=1/8, and selected semiconductor mode-locked pulsed laser (1) each wavelength meets following condition:

$\frac{2\mathrm{\π}}{{\mathrm{\λ}}_{n-1}}\·n_o\left({\mathrm{\λ}}_{n-1}\right)\·L-\frac{2\mathrm{\π}}{{\mathrm{\λ}}_n}\·n_o\left({\mathrm{\λ}}_n\right)\·L=\frac{\mathrm{\π}}{2^{N_b-1}}$

In formula, N _bfor the quantified precision of this A/D conversion system.Then from the light signal be through quantizing that each n × 1 demodulation multiplexer (7) different wave length channel exports, it is converted into electric signal through photodetector (8), send in comparer (10) and adjudicate after being amplified by amplifier (9), gained exports the scale-of-two be through reaction simulation signal (3) Real-time intensity of coding and to go in ring code.For 4 wavelength, namely during semiconductor mode-locked pulsed laser (1) medium wavelength number n=4, quantification and the encoding characteristics of full optical analog to digital conversion scheme shown in Fig. 4 can be expressed as shown in Figure 5.

When carrying out the upgrading of quantified precision to the A/D conversion system described in Fig. 4, first method the core component (11) in low-order system is replaced with the multi output passage core component (11) with certain phase shift relation produced by multiple 8 × 8 multi-mode interference couplers (15) cascade, and cascade m 8 × 8 multi-mode interference couplers (15) need use 1 × m multi-mode interference coupler (4) and passive phase shift waveguide.The number of corresponding n × 1 demodulation multiplexer (7) increases along with the increase of digital output channel number.Second method is the number increasing different wave length laser instrument in semiconductor mode-locked pulsed laser (1).The third method is the number both having increased different wave length laser instrument in semiconductor mode-locked pulsed laser (1), again core component (11) is replaced with the high-order quantization system produced by multiple 8 × 8 multi-mode interference coupler cascades.Such as, be promoted to 6 quantified precisions by 5 quantified precisions, the core component (11) in Fig. 2 can be replaced with the core component shown in Fig. 7 according to first method, the passive phase shift waveguide used by cascade is the passive phase shift waveguides (15) in π/8; The number of different wave length laser instrument in semiconductor mode-locked pulsed laser (1) can be increased to 8 by 4 according to second method; Core component (11) in Fig. 2 is replaced with the core component shown in Fig. 7 according to the third method simultaneously, and the number of different wave length laser instrument in semiconductor mode-locked pulsed laser (1) is increased to 8 by 4, then the quantified precision theoretical value of gained A/D conversion system is 7.By that analogy, the final quantization precision N of system _bwith 8 × 8 multi-mode interference couplers (15) quantity N used in semiconductor mode-locked pulsed laser (1) wavelength number n and core component (11) _{mMI8 × 8}relation be shown below:

N _b=log ₂(8N _MMI8×8·n),N _MMI8×8=1,2,3,...,n=1,2,3,...

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and replacement, these improve and replace and also should be considered as protection scope of the present invention.

Claims (7)

1. a full optical analog to digital conversion method for designing, is characterized in that, comprise the following steps:

S1, by multi-Wavelength Pulses light source produce multiplex pulse light be multiplexed in same light path by multiplexer;

S2, by 1 × 2 multi-mode interference coupler, above-mentioned light path is divided into 2 tunnels again, the analog optical signal of phase-modulator to input of wherein leading up to is sampled, enter in an access interface of multi-mode interference coupler afterwards, another access interface of multi-mode interference coupler is directly injected on another road;

S3, be demultiplexed on the optical channel of different wave length by the light that the output port from described multi-mode interference coupler exports through demodulation multiplexer, the light signal exported from described demodulation multiplexer is exactly the light signal after being quantized and encoding;

S4, the light signal using photodetector, amplifier and decision device to export described demodulation multiplexer successively receive, amplify and adjudicate, and obtain binary digital output signals;

Wherein, by increasing the sampling pulse source number of different centre wavelength or increasing the number of multi-mode interference coupler, analog-to-digital quantified precision can be improved;

Wherein, described multiplexer/demultiplexer is realized by array waveguide grating.

2. the method for claim 1, is characterized in that, described multi-mode interference coupler is 4 × 4 multi-mode interference couplers or 8 × 8 multi-mode interference couplers.

3. the method for claim 1, is characterized in that, described multi-Wavelength Pulses light source is realized by Mode-locked laser device.

4. the method for claim 1, is characterized in that, described phase-modulator is realized by electroded active optical waveguide.

5. the method for claim 1, is characterized in that, the device that the method uses can realize integrated on InP-base, GaAs base or Si base.

6. the method for claim 1, is characterized in that, the quantification of the method and cataloged procedure are realized by 4 × 4 multi-mode interference couplers or 8 × 8 multi-mode interference couplers.

7. the method as described in claim 2 or 6, is characterized in that, described 4 × 4 multi-mode interference couplers or the input waveguide of 8 × 8 multi-mode interference couplers and the selection of output waveguide have following rule:

For 4 × 4 multi-mode interference couplers, its input waveguide is combined as the 1st passage and the 3rd passage, or the 2nd passage and the 4th passage, and its output waveguide is combined as the 1st passage and the 3rd passage, or the 2nd passage and the 4th passage;

For 8 × 8 multi-mode interference couplers, its input waveguide is combined as the 1st passage and the 3rd passage, or the 6th passage and the 8th passage, and its output waveguide is combined as 1,2,3,4 four passage, or 5,6,7,8 four passages.